When metereologists make cherry blossom forecasts, they are referring to the Somei Yoshino variety which has a very short season — from late March to early April, to be exact. However, hanami forecasts don't usually include the early or late-blooming cherry trees, which are also quite lovely.
Yaezakura, which means "multi-layered cherry blossom," is a catch-all term for cherry blossoms with more than five petals. Starting to bloom in mid-to-late April, yaezakura have petals that range from light to dark pink. Because of the double layers of petals, they are known as a symbol of strength — in comparison to the delicate and fleeting Somei Yoshino.